This invention relates to a DC-DC converter, comprising a controllable switch for producing at least one output voltage, the duty cycle of the controllable switch being controllable by means of a microprocessor.
The powering of electronic apparatus requires the use of DC-DC converters which supply one or more output voltages. DC-DC converters comprising a controllable switch are clocked DC-DC converters, among which notably flyback converters and forward converters can be distinguished as basic types. Therein, an input DC voltage is converted, using the controllable switch, into a squarewave voltage which is rectified and filtered. The controllable switch can operate, for example, at frequencies of between 50 kHz and 200 kHz. The controllable switch is controlled by pulses whose respective width, characterizing the duty cycle, is modulated in dependence on load fluctuations of the output voltage. The pulses are generated by a control circuit, for example a pulse width modulator and are applied to the control electrode of the controllable switch. The duty cycle is then usually varied at a constant switching frequency of the controllable switch.
GB-A-2 030 736 proposes to control the duty cycle of the controllable switch in a DC-DC converter of the kind set forth by means of a microprocessor. Therein, quantized values which determine the duty cycle are applied to a driver stage which drives the controllable switch. In order to avoid instabilities in the control of the DC-DC converter, a comparatively fast and hence expensive microprocessor must be used.